I did extensive research before purchasing a tankless water heater. The common problem seems to be that people are reading the GPM a unit is capable for their area and are expecting a nice hot shower. The GPM listed is based on heating water to only 105 degrees which is nice and warm out the unit, but by the time it gets to the other end of the house, it is barely body temp, if that. We found it needs to output between 120 and 125 degrees to get a nice hot shower (using no cold water). This in turn ups the kW required to heat the water... So to be safe, I picked the biggest model available right now (36 kW) and are tickled to death over the performance. It is solid, steady source of hot water for both showers at the same time. Love it. -- Note: If you don't have four 40 amp breaker slots available, no problem! Still get this bad boy and start off with 2 or 3 circuits(whatever you have available) and it'll use what you give it (albeit you may have to limit use to just one item at a time)... allowing you time to wire up for more power later.

UPDATE (5/15/2016): It had performed flawless for about 4 months. Then, suddenly, one day it said "OFF" and nothing we did (even with tech support via phone/email) fixed the problem. So, we had 3 days of cold water in the home until a new controller card arrived. Installed it (pretty easy) and voila! we're back in business. Tech support was easy to reach and the part was delivered via 2-day service. However, since then, it has turned itself completely off (not even light up) for no apparent reason. No breakers tripped... but recycling the breakers restored service. It has been a month now since last time it did that. -- I am still very happy with the purchase and would recommend it for anyone thinking about trying it.

I purchased 2 of these ECO 27's in early 2012 and a similar model ECO 18; please see my previous reviews. One unit has now failed due to a leaking heat exchanger; an internal plumbing connection located at the weakest point - a soldered copper pipe - eventually broke loose. The terms of the warranty were not posted on the Ecosmart website. Upon receiving the units and reading the enclosed warranty, it was apparent that there were strict requirements to qualify the units for the warranty; warranty cards had to be returned within 30 days, and the installation had to be by both a licensed plumber and a licensed electrician, whose names, phone numbers, and license numbers had to be noted on the warranty cards.

This posed problems for my application since 1) the installation was for a remodeling project and could not be completed in the next 30 days 2) the area where the home is located does not require licensed electricians or plumbers for remodeling work (and none were going to be hired to install a water heater, as I have those skills myself, having renovated 27 homes previously and I have college degrees and construction trade experience in those fields). Therefore I wrote a letter to Ecosmart asking for exceptions to the requirements, else I wanted to return the units for credit. I received an email response from the then-Director of Operations Mr. Nicholas Cardoso who stated, as directly copied below:

"As long as the units are properly stored there will not be a problem. When the units are installed just send in the registration information and we will document all the information should you need assistance in the future. If you have any questions let me know.
Thanks.
Nicholas Cardoso
Director of Operations
ECOSMART US, LLC
3315 NW 167th Street
Miami Gardens, FL 33056
PI 305.623.7900
FI305.623.7923
www.ecosmartus.com"

It is my understanding from web information that Mr. Cardoso later became the CEO of the company and is still employed by them although the company was sold.

I returned the 3 warranty cards within 90 days, once the units were installed, and retained the customer half of each card, as was required.

So when one of the units failed recently, I contacted customer service, and during 3 emails and 3 phone calls over 1 week was told that Ecosmart only sends out repair parts for these units, not replacement units. Therefore the customer must remove and disassemble the internals of the units to repair them himself. This requires the customer to have electrical and plumbing experience and proper tools for disassembly. Furthermore, the heat exchanger - the part that failed - is not available as a replacement part. And finally, I was told that Ecosmart had an old database that may contain my records, but the current database has no records of my purchases nor their receipt of my warranty cards. IN OTHER WORDS, THERE IS NO WARRANTY EVEN WHEN THE CUSTOMER RECEIVED PERSONAL ASSURANCE OF A WARRANTY FROM THE CEO OF THE COMPANY. I asked to speak with Mr. Cardoso but was not allowed access to him.

Now you know why Ecosmart wont post the terms of their warranty on their website. BUYER BEWARE.

With the life of these units being about 3 years, and since the units have unique, non-industry-standard electrical and plumbing connections, which makes quick replacement labor-intensive and/or impossible, you should buy a spare of these to keep on hand when one fails.

I ordered a replacement from Amazon. Incidentally, the new unit has the same internal copper tubing design flaw as the old one, and still has an incoming wire clamp connector that wont meet electrical codes because electrical conduit, not unsheathed #8 wires, is required for the installation; the cable entrance hole in the panel is not large enough to accommodate a conduit connection for those wires. Takes a large hole punch and/or a Dremel tool to enlarge the existing hole so that a conduit connection can be made.

Picture shows where the weak point is that leaks over time. It is the center connection between 2 heat exchanger tubes.

Units do work well when they work. Just buy a spare, as you'll eventually need it.

I've bought 2 of these, the first worked great supplying a bath and kitchen. The second one I received was obviously used and put back in the box ( it even had paint on the connection cable from where it had been installed). I called Amazon and they were great about getting another shipped that same day. I like this unit better than the Rheem (of the same capacity) because this unit has 2 elements where as the Rheem has only one. This unit can use one element at low flow rates and kick in the second as needed. Please note, you will need number 6 wire and a 60 amp double breaker to power this unit. Also note, EcoSmart does not provide a warranty unless you have a licensed plumber and electrician install the unit. The warranty registration has a space for the signatures and license numbers. If you are going to install it yourself this may be important, as you will not have a warranty. Operation is excellent, make sure you flush the lines as they recommend to remove any air, and then set the temperature after you power up the unit.

Before getting this, I read a number of reviews on other Ecosmart tankless water heaters. Some were very positive reviews, but others were negative and mentioned getting used/defective units and having poor customer service. I'm happy to say that the one that I got was clearly brand new and factory fresh, and that Ecosmart's customer service responded early the next business day when I contacted them over e-mail about an installation question.

SUMMARY
-----------
This unit is a well-made system with a lot of heating capacity. I'd say it's five stars if you know what you're getting into and it fits your needs, but you definitely might like it a lot less if you don't know all the facts before paying (currently) $650 for it and then finding out it's not what you wanted. This is a nice unit, but it's not for everyone, and I'd like to try and help you decide if it is a good fit for your needs. As a result, my review below is broken into three parts: (1) some things to consider before buying this type of system, (2) my impressions of this specific unit, and (3) the simple math you can do to help decide what sized unit to buy if you decide tankless is the way to go for your home.

The video is just a quick overview of the unit, both as delivered and in operation, so that you can get a look at it and the internal construction. It also has a table of numbers to supplement one of my points below on usage considerations.

I learned a number of things after ordering it and getting it set up, and the end result is that I'm going to stick with my tank system for now. One reason is that it doesn't support warm or hot water at fairly low flow conditions (that's the table of numbers in the video). That's specific to my desires and may not matter to you. Another reason is the full cost of running the electrical lines that I had not thought through - so I point it out to you below.

If you have any questions/comments, assuming that you're still awake after all of this :D, please feel free to leave a comment and I'll respond as soon as I can. Thanks!

CONSIDERATIONS
---------------------
I'm no Bob Vila, but there are some things that I'd like to point out. Some of these I hadn't fully thought through or didn't know before ordering the unit, so I wanted to share.

(*) POWER REQUIREMENTS
Be absolutely sure to consider the power requirements for this unit and the cost/time for installation. The product description here on Amazon emphasizes that this requires 150A of dedicated service. More specifically from the installation manual, you will need to run four 240V, 40A lines to this heater if you want to use the full 36 kW of capability. That means four double-pole (240V) 40A circuit breakers and #8 copper wiring (12 wires total, eight "hot" wires and four ground wires). At my house, that's about $250 in raw materials alone before even paying someone to install/inspect the electrical lines, so not a trivial consideration for me. Also, they recommend at least 200A of total house electrical service. I recommend checking your electrical box to make sure that you have enough room to accommodate four double-pole breakers, and also double check if your total service is at least 200A.

Now, this is the current big daddy of Ecosmart's heater line, and it has a lot of capacity. The good news is that it's designed to run off of anywhere between one and four 40A lines, so you don't actually need to hook up all four lines. Of course, the fewer lines you run, the lower the capacity will be - but you can run this off of one single 240V, 40A line. Even at just one line, you've got 9 kW of heating capacity. So, you don't get all of the benefit with fewer lines, but it's an opportunity to buy a unit that you may grow into without having to run all of those power lines right in the beginning. That's the good news. The potentially bad news is if you're like me, you don't even have one 40A line running to your water heater. If you have an electric water heater with a tank already, you probably have a single 240V, 30A line run to that location. 30A lines typically use smaller wires, so you probably would need to run all new wiring regardless to prevent the copper lines in your walls from overheating.

Another note on power: this unit is only going to draw as much current as is needed to heat the water up to the set point. It doesn't draw max current and then back off like a boiler might because that would overheat the water. It also doesn't pulse the heaters on/off, drawing max current in pulses. So, you aren't going to dim your lights every time you turn on the hot water. :) The 150A "requirement" is if you use this to its full potential. That said, power draw certainly may not be trivial. For example, if you're incoming cold water temperature is 60 degrees F and you'd like to take a shower at 105 degrees F with a 2 GPM flow rate, this unit is going to draw about 55A (so you'd need at least two 40A lines run to it).

(*) USAGE LIMITATIONS
The only one that comes to mind, but it's one that I didn't know about until I got the unit and really went through the manual (and verified after hooking it up), is that it will not turn on and begin heating water until the flow rate is greater than ~0.25 GPM (gallons per minute). Now, that's water flow on the hot water line - not total water flow. So, even if you turned your faucet all the way to hot, you'd have to have at least 0.25 GPM of flow before the heater would start to heat up the water. If you had the faucet at the midpoint between hot and cold, you'd need 0.5 GPM of total flow...and so on. I included an example table in the video to show this for one set of temperatures. I think this is definitely something to consider if you want warm (not hot) water at lower flow rates sometimes or occasionally use a trickle of hot water like I do to wash some things.

(*) NOT "INSTANT" HOT WATER
A whole-house tankless heater is different from a point-of-use heater like what you'd install under a sink. Any delay that you have now in waiting for water to get hot at your faucet is going to be the same with this versus a tank, assuming that you install this in the same location as your current tank. Might sound like common sense, but some folks that I've talked to about this just have a mental impression about tankless heaters being instant hot water, so I'm pointing it out. The delays in water getting hot at your faucet are caused by flushing out the water already in the lines when you turn on the faucet, along with some level of heating up the water pipes so they aren't cooling off the water much on it's way to the faucet. Tank or tankless, that still happens. If you want essentially instant hot water, a point-of-use heater is the way to go.

(*) INSTALLATION
It should go without saying, but either get a certified plumber and electrician to do the install, or have your work inspected to make sure that it meets code in your area. You can void the warranty on the unit if you don't.

MY ECO 36 IMPRESSIONS
-----------------------------
Overall, I'm impressed by the build quality, ease of installation (once you have the electrical lines in place), and customer service.

(*) HARDWARE DESIGN AND BUILD QUALITY: 5 Stars
I'm not a professional plumber, but the workmanship looks very good and solid to me. The external case is well made, and it's easy to get the cover off to work on this inside. Everything on the inside is laid out neatly and assembled cleanly. The heating elements are designed to unscrew for removal and replacement if needed, which is nice and prevents you from having to replace the entire unit if one goes bad.

Hook up of the electrical lines is straightforward and easy to do. Just three locations to insert wires and tighten a screw to secure them for each 40A line (two "hot" wires and a ground wire). The screw-down locations for the wires are located right by the opening in the case for the wires, and the case comes with a strain-relief clamp. I had no issues securing the wires or adjusting the strain relief on my unit.

Hooking up the water lines couldn't be much easier. The one thing that I would have liked to have seen was more area on the outside of the case to grip the pipes as I secured the water lines to prevent putting stress on the internal components in the heater. There was plenty of area right inside the case to grip those pipes, but it means that the lid had to be off to properly properly secure the water lines. No biggie, and the only nit on installation that I had.

(*) CONTROL PANEL DESIGN: 4 Stars
As far as water heaters go, it's probably more like 5 stars. It's very easy to operate and to read, and you can't really mess anything up - you either turn it on/off or you adjust the temperature set point. Very straightforward.

I took one star away because of what I wish they had included, which is the ability to see some of the parameters being monitored by the controller. I'd really like to see a read out of the current water flow rate, the incoming water temperature, the outgoing water temperature, and the power draw. They wouldn't need to add another display, either, but just some way to toggle that info (like a separate, smaller button). I know folks wouldn't use that often, but it would probably be easy to do and would be really helpful when doing diagnostic work and when first setting it up.

(*) CUSTOMER SERVICE: 5 Stars
So far, five stars in my book. I sent an inquiry about installation via their website e-mail late in the day on Christmas Eve, and I received a response the morning after Christmas. They first attempted to call me, and when I didn't get to the phone in time, the rep left me a voice mail with information and call back numbers, and then almost immediately sent an e-mail with a detailed answer to my question. He answered my question thoroughly, and I was quite pleased. I have not had to contact them about any problems with the unit, so I don't know that part of their service.

A (VERY) LITTLE MATH
--------------------------
Ecosmart provides some good examples of capacity, but their diagram on this page doesn't include the ECO 36 as of my review because (I'm guessing) it's such a new product. So, here is some fairly quick and simple math that you can do to figure out if this is a good unit for you, or if it's too much (or too little) for your needs. I've already input some of the parameters into the equation below to help simplify it for you. The equation is not exact, but it's a very close approximation.

POWER EQUATION: Approximate power required (in W) = 146.5 * Water Flow Rate (in GPM) * Water Temperature Rise (in degrees F)

For example, if your cold water is at 60 degrees F and you want 2 gallons per minutes of water at 105 degrees F for a shower, the power required is:
Power required = 146.5 * 2 * (105 - 60) = 146.5 * 2 * 45 = 13185 W = 13.2 kW, or a little over a third of the capability of this unit.

The current draw in amps is just the power (in Watts, W) divided by the voltage (which is roughly 240V in this case). In our example, your shower would require about 55A for most of the shower. However, if your set point is higher than what you'd use in the shower, but you turn the water all the way to "hot" to get the shower ready, then the unit is going to draw enough power to warm up 2 GPM at the temperature difference between your set point and (in our example) 60 degrees F. So, if your set point is 125 F, then that would be 146.5 * 2 * (125 - 60) = 19000 W, or about 80A, until you turn the water temperature in the shower down to 105 F.

The Good
As for the item itself I would only suggest that the purchaser make sure they have sized the unit correctly for their needs and have taken their area's ground water temp into account. The unit has a sublimely simple design and its shell is both space efficient and cosmetically pleasing. Unlimited hot water is a decadent luxury and Ecosmart makes it affordable to all. My lady is finally able to take her time wash and shave without ever running out of hot water (yikes for my water consumption). Regarding water consumption I'v found that this unit works amazingly well with the "Spa Fire-Hydrant" shower head, Economy and Performance.
The Bad
This pertains to the install process and NOT the unit. -- The plumbing is very straight forward and should be doable by a moderately experienced DIY'er with basic plumbing tools and a little soldering know-how. The Electrical is also not very difficult BUT requires two Double Pole 40-Amp Breakers and sufficient sized service to handle the unit (which is actually comparatively large). But if you've got the space or are willing to upgrade your electric service this item is a must-have.
Final Warning
The large cost for this unit will come from the install by licensed professionals without which you cannot quality for the lifetime Warranty, My advice (if you are not planning to install yourself) would be to get quotes for the install (both plumbing and electrical) and compare those numbers to the cost of the unit if you end up paying more for the install than the unit is worth you might be better off forgoing the warranty because if you do have a problem it would still be cheaper to by a replacement unit.

***One year Update
I've had this unit for a year now and recently blew a heating element, (an issue caused by a plumbing change and NOT the unit itself). I only bring it up because its a bit of a pain to have to order a replacement from Eco-Smart since no other place I found (Even Amazon!) carries this odd element size (9kW 240v Screw-In). So I would suggest having a spare on hand to avoid the shipping time wait if it becomes necessary. Also having seen first-hand what kind of scale and build up can occur at tragic speeds on the heating elements, do yourself a favor and drop the extra $65 on the recommend 'Aqua-pure' scale inhibitor. Most users can only tell you that it seems to work having nothing to compare it against. I have seen both sides and it makes a world of difference!
Aside from that, I am Extremely happy with this purchase, there is no going back in my household, Even with my girlfriend's new 45 minute long shower ritual (compared to the 25ish she use to get), I have seen a consistent 20-30% electric consumption drop when compared to the two years proceeding it. So my unit will have paid for itself after another year of usage. If your experience is anything like mine you will NOT be disappointed with this unit, so I'd say buy with confidence